The long term objectives of this research plan continue to be a concise delineation of the physiology and pharmacology of sensory neurons in the dorsal horn of the spinal cord of physiologically intact, awake, drug free, restrained cats. Recent advances in our understanding of the anatomy, physiology and pharmacology of the spinal cord have revealed a complex system which provides, among other things, important sites at which ascending pain signals may be modulated. In order for us to completely appreciate how such modulation occurs, and thus improve clinical approaches to selective spinal analgesia, it is imperative that we understand how the systems work in the physiologically intact, animal. This project has reached a point where it is now possible to both record electrical activity from single neurons in the dorsal horn of intact animals as well as study drug effects on the recorded electrical activity. Although this new technique opens the door to many important and interesting studies, it is imperative that emphasis first be placed upon a determination of the normal physiologic response profiles of neurons involved with the afferent transmission of information at the level of the spinal cord. As such, the specific aims of this project are simple and straightforward. The first aim is, using this newly developed, extracellular, single neuron, microelectrode recording technique, to continue the characterization of the neurophysiologic response profiles of dorsal horn spinal cord neurons in physiologically intact, awake, drug free, restrained cats. These studies will determine receptive field characteristics of these neurons as well as neuronal response characteristics of both spontaneous activity and of activity evoked by both non-noxious and noxious peripheral stimulation. The second aim is to determine the effects of selected drugs upon those physiologic responses. Acquisition of the above information will serve two important functions. First it will provide background information on the normal physiology and pharmacology of afferent transmission in the spinal cord that will be a starting point for wide ranging studies of spinal cord pharmacology, especially as it relates to pain modulation. Secondly, it will clarify the influence of acute preparations (anesthetized, decerebrate, spinal cord transected) on our understanding of spinal cord function.